A pneumatic brake booster equipped with a damping device is discussed in patent document FR 0015542 describes a pneumatic brake booster of the type described above, with a cylindrical helical or conical spring equipped with a damper to reduce or eliminate the vibrations of the return spring pushing the drive piston into its rest position.
Several embodiments of this damper are described in the document. A first embodiment of the damper is a sleeve affixed to the wall of the forward chamber, supported by the forward extremity of the return spring. It forms a sleeve with a curved bead against which the coil of an extremity of the spring rests, holding this bead against the interior wall of the brake booster housing. This rubber damper acts through friction and by elastic extension.
The document describes another embodiment of a damper consisting of a clamp surrounding two or more coils. These are simple, possibly non-extensible, even rigid clamps that, according to the indications provided by the document, impose a shift of the resonance frequency to a value where the vibration could no longer be sustained.
These solutions do, of course, dampen the return spring vibrations, but their implementation is relatively complicated because of the need to place them on the spring more or less installed in the housing of the brake booster or between a portion of the housing and the spring, and their effectiveness is reduced because they operate by friction.